CVE-2026-39871: Apple macOS Information Disclosure Flaw

CVE-2026-39871 Overview

CVE-2026-39871 is a path handling vulnerability in Apple macOS that allows an application to observe unprotected user data. The flaw is categorized under [CWE-552] (Files or Directories Accessible to External Parties). Apple addressed the issue by improving path handling logic in macOS Sequoia 15.7.7, macOS Sonoma 14.8.7, and macOS Tahoe 26.5. The vulnerability impacts data confidentiality but does not affect integrity or availability.

Critical Impact

A malicious or curious application running on an affected macOS system can observe user data that should remain protected, leading to information disclosure without requiring user interaction.

Affected Products

• Apple macOS Sequoia (prior to 15.7.7)
• Apple macOS Sonoma (prior to 14.8.7)
• Apple macOS Tahoe (prior to 26.5)

Discovery Timeline

• 2026-05-11 - CVE-2026-39871 published to NVD
• 2026-05-12 - Last updated in NVD database

Technical Details for CVE-2026-39871

Vulnerability Analysis

The vulnerability stems from improper path handling within macOS. An application can leverage flawed path resolution logic to access user data that should otherwise be isolated from third-party processes. Apple's advisories describe the issue as a logic flaw resolved through stricter path validation.

The weakness aligns with [CWE-552], which covers files or directories that are made accessible to parties that should not have read access. Because the attack vector is rated as network-reachable with no privileges or user interaction required, an installed or sandboxed app could trigger the condition during normal operation.

Exploitation results in disclosure of sensitive user data. There is no integrity or availability impact, meaning attackers cannot modify files or crash the system through this flaw alone. However, exposed data may include credentials, tokens, or personal files that enable follow-on attacks.

Root Cause

The root cause is inadequate validation when resolving file system paths. Apple's fix description specifies that the issue was addressed with improved logic, indicating the prior implementation did not correctly enforce access boundaries on certain path constructions.

Attack Vector

An attacker delivers or installs an application on the target macOS device. Once executed, the app abuses the path handling weakness to read user data outside its intended access scope. No elevated privileges or user prompts are required during exploitation.

No verified proof-of-concept code is publicly available. Apple has not disclosed implementation specifics beyond the advisory text. Refer to the Apple Security Advisory 127115, Apple Security Advisory 127116, and Apple Security Advisory 127117 for vendor details.

Detection Methods for CVE-2026-39871

Indicators of Compromise

• Unsigned or recently installed applications accessing user directories outside their declared sandbox entitlements.
• File system access events targeting protected paths such as ~/Library, ~/Documents, or app group containers from unexpected processes.
• Unusual read operations on user data shortly after application launch, particularly from apps not granted Full Disk Access.

Detection Strategies

• Monitor Endpoint Security framework (ES_EVENT_TYPE_NOTIFY_OPEN) events for processes reading sensitive user files without corresponding TCC prompts.
• Audit installed applications and their requested entitlements against actual file system behavior to identify privilege boundary violations.
• Correlate process execution telemetry with file access events to identify path traversal or symbolic link abuse patterns.

Monitoring Recommendations

• Enable unified logging audit trails for file system access events on critical macOS endpoints.
• Track installation of new applications and review their first 24 hours of file system activity.
• Alert on processes accessing TCC-protected directories without recorded user consent grants.

How to Mitigate CVE-2026-39871

Immediate Actions Required

• Update affected systems to macOS Sequoia 15.7.7, macOS Sonoma 14.8.7, or macOS Tahoe 26.5 immediately.
• Inventory macOS endpoints in your environment and prioritize patching for systems handling sensitive user data.
• Restrict installation of untrusted applications via mobile device management (MDM) policies until patching is complete.

Patch Information

Apple released fixes in macOS Sequoia 15.7.7, macOS Sonoma 14.8.7, and macOS Tahoe 26.5. Patch details are available in Apple Security Advisory 127115, Apple Security Advisory 127116, and Apple Security Advisory 127117. Deploy these updates through Apple Software Update or your MDM solution.

Workarounds

• Limit application installations to vetted sources such as the Mac App Store or notarized developers until patches are applied.
• Enforce TCC (Transparency, Consent, and Control) policies via MDM to restrict access to user data directories.
• Audit existing applications for unnecessary file system entitlements and revoke broad access where possible.

# Verify current macOS version and apply available updates
sw_vers -productVersion
sudo softwareupdate -l
sudo softwareupdate -ia --restart